Dr. Farid Fata, a Michigan oncologist, has been convicted for misdiagnosing hundreds of patients to fool insurance companies. An office manager for Dr. Fata has revealed how the doctor was exposed with the help of staffers for defrauding insurance companies.

George Karadsheh, who worked for Dr. Farid Fata's Crittenton Cancer Center in Rochester Hills, Michigan, said he smelled something going wrong as staffers kept leaving the practice. Karadsheh came to know that a different oncologist in the practice was leaving and couldn't stop himself from asking him the reason, learning that Fata was administering chemotherapy to patients who didn't need it.

"He was also explaining that patients who were on hospice were taken off hospice and put on chemotherapy, put back on chemotherapy. He also pointed out that patients who were receiving chemotherapy without disease were receiving it to the very last day of life", Karadsheh told ABC News.

Fata, who was trained at Memorial Sloan-Kettering in New York, had earned the trust in the community which is why it was difficult to believe that he was involved in such a shameful act, Karadsheh added.

Karadsheh said that Fata's arrest is in the interest of public and he is so relieved that he has been punished for his wrongdoings.

FBI agents arrested Fata on Aug 6, 2013, and he has been sentenced today to 45 years in federal prison. Fata was convicted for often prescribing treatments for cancer to patients who didn't have it. So far, at least 553 victims had been identified.